Residential cooking fires remain a significant source of property damage and injury. According to Consumer Product Safety Commission (CPSC) staff estimates, all cooking equipment-related fires account for nearly 40% of all residential fires that were attended to by a fire department while range/oven, non-confined fires account for approximately 14,600 incidents per year (D. Miller and R. Chowdhury; 2006-2008 Residential Fire Loss Estimates; U.S. Consumer Product Safety Commission, 2011). Government funded research has demonstrated that food and pan-bottom temperatures are reliable indicators of pending ignition.
One approach to mitigate cooking fires is based on the history of testing and analysis that shows that limiting the pan temperature to roughly 700° F. or below will avoid temperatures at which the preponderance of fires from ignition of food in a cooking vessel will occur.
The challenge has been to limit the pan temperature at or below approximately 700° F. while ensuring that the heating rate remains high enough that heat times, boil times, and high temperature cooking methods are not compromised. An acceptable implementation of the temperature limit should not compromise cooking modes including: boiling, searing, sautéing, frying, blackening, or simmering.
U.S. Pat. No. 5,796,346 to Walsh describes a stove including circuitry to facilitate avoidance of fires such as may be caused by grease or another flammable substance present on the stove burner. The control shuts the element off when a time limit is reached while operating at power level above a predetermined threshold that could lead to the pan reaching an ignition temperature of grease. Time is not a sufficient indicator of fire risk as the time to reach the ignition temperature can vary with element power, pan size and type, oil amount, etc.
U.S. Pat. No. 8,001,957 to Clauss describes the opposite of this approach, in which the gas burner operates at a maximum level except for a limited period of time over which a booster can be used to temporarily allow an increase in gas flow rate and therefore burner power. The basic gas cooking hob is enhanced with a timing member which allows the heating power to be increased beyond the nominal power during a certain interval. Fire is mitigated by preventing a high power level for an extended period of time. This is not sufficient to catch high pan temperatures when the hob is at its standard, maximum level.
U.S. Pat. No. 4,812,625 to Ceste describes a temperature control system for cooking apparatus, for example, a fryer using cooking oil or shortening which is heated by a suitable heating element. The cooking apparatus has different modes of operation including start-up mode, idle mode and cooking mode. Overshoot to a temperature above the setpoint temperature is limited during start-up mode, idle mode and cooking mode with the apparatus having different temperature control characteristics based on the mode of operation and adapting variable parameters to achieve optimum temperature control accuracy. But in this case, the cooking medium, i.e. the cooking oil has a temperature sensor reading its temperature directly. An alternative approach is needed when the temperature of the oil cannot be read directly, as is the case when the oil is inside a pan and the pan is heated by the hob.
U.S. Pat. No. 6,663,009 to Bedetti describes a configuration of sensors around a gas flame to detect pan temperature and control heat output of the burner, but does not identify an algorithm that would be able to mitigate a safety problem from this temperature sensor input.